432 research outputs found
Increasing the wear resistance of ultra-high molecular weight polyethylene by adding solid lubricating fillers
In order to compare effectiveness of adding solid lubricating fillers for polymeric composites based on ultra-high molecular weight polyethylene (UHMWPE) with graphite, molybdenum disulfide and polytetrafluoroethylene, their tribotechnical characteristics under dry friction, boundary lubrication and abrasive wearing were investigated. The optimal weight fractions of fillers in terms of improving wear resistance have been determined. The supramolecular structure and topography of wear track surfaces of UHMWPE-based composites with different content of fillers have been studied
Increasing the wear resistance of ultra-high molecular weight polyethylene by adding solid lubricating fillers
In order to compare effectiveness of adding solid lubricating fillers for polymeric composites based on ultra-high molecular weight polyethylene (UHMWPE) with graphite, molybdenum disulfide and polytetrafluoroethylene, their tribotechnical characteristics under dry friction, boundary lubrication and abrasive wearing were investigated. The optimal weight fractions of fillers in terms of improving wear resistance have been determined. The supramolecular structure and topography of wear track surfaces of UHMWPE-based composites with different content of fillers have been studied
Comparison of mechanical and tribotechnical properties of UHMWPE reinforced with basalt fibers and particles
Mechanical and tribotechnical properties of UHMWPE composites reinforced with basalt fibers and particles under dry sliding friction and abrasion were investigated. It is shown that adding of the basalt particles provides higher wear resistance under the dry sliding friction while at abrasion filling by the basalt fibers is more efficient since the wear resistance of the reinforced UHMWPE composites is by 3.7 times higher in contrast with the neat polymer. Wear mechanisms of the polymeric UHMWPE composites under various types of wear are discussed
Controlling the Frequency-Temperature Sensitivity of a Cryogenic Sapphire Maser Frequency Standard by Manipulating Fe3+ Spins in the Sapphire Lattice
To create a stable signal from a cryogenic sapphire maser frequency standard,
the frequency-temperature dependence of the supporting Whispering Gallery mode
must be annulled. We report the ability to control this dependence by
manipulating the paramagnetic susceptibility of Fe3+ ions in the sapphire
lattice. We show that the maser signal depends on other Whispering Gallery
modes tuned to the pump signal near 31 GHz, and the annulment point can be
controlled to exist between 5 to 10 K depending on the Fe3+ ion concentration
and the frequency of the pump. This level of control has not been achieved
previously, and will allow improvements in the stability of such devices.Comment: 17 pages, 10 figure
Structure and tribomechanical properties of extrudable ultra-high molecular weight polyethylene composites fabricated by 3D-printing
Antiradical, Antimetastatic and Antitumor Activity of Kaolin Preparation “Kremnevit”
The objective of the research was to determine antiradical, antimetastatic and antitumor activity of kaolin preparation “Kremnevit”.Material and methods. Experiments were carried out on 30 male C57BL mice inoculated with Lewis lung carcinoma (LLC) cells. The rate of superoxide radical generation in tumor cells as well as in animal organs was determined using 1-hydroxy-2,2,6,6-tetramethyl-4-oxopyrrolidin- hydrochloride spin traps and electron spin resonance (ESR) spectroscopy at room temperature.Results of the experiments showed that the preparation “Kremnevit” exhibits antitumor activity reducing the tumor mass by 24% in experimental animals compared to animals which did not receive the preparation. “Kremnevit” affects the rate of superoxide radical generation by intracellular (mitochondria) and extracellular sources (the NADPH oxidase of tumor-associated neutrophils (TANs). The superoxide-generating activity of TANs increased in mice treated with “Kremnevit” compared to animals which did not receive it.Conclusions. Non-toxic kaolin preparation “Kremnevit” has antitumor and antimetastatic activity regulating electron transport in hepatocyte mitochondria during superoxide radical generation by hepatocyte mitochondria and immunocompetent blood cells of mice inoculated with LLC cells.
Scale effects in tribological properties of solid-lubricating composites made of ultra-high molecular weight polyethylene filled with calcium stearate particles
Friction properties being influenced by scale effects are simulated in the paper by the example of polymer composite material made from Ultra High-Molecular Weight Polyethylenes (UHMWPE) filled by calcium stearate (C[36]H[70]CaO[4]). Of interest are the composites whose mechanical properties and tribotechnical characteristics do not depend monotonically on filler (inclusions) weight fraction. In order to describe the influence of scale effects onto frictional properties the model based on Reiss averaging (model of "weak phase") is employed. It is also suggested that when gradient elasticity theory is applicable the formal analogy between effective friction coefficient for surface heterogeneous structures and effective mechanical properties (compliances) for heterogeneous material can take place. Theoretical dependence to describe nonmonotonic change of effective friction coefficient versus filler concentration was obtained for the polymer composites under study. The suggested expressions might be useful for the sake of properties prognosis of antifriction polymeric materilas
Creating traveling waves from standing waves from the gyrotropic paramagnetic properties of Fe ions in a high-Q whispering gallery mode sapphire resonator
We report observations of the gyrotropic change in magnetic susceptibility of
the Fe electron paramagnetic resonance at 12.037GHz (between spin states
and ) in sapphire with respect to applied magnetic field.
Measurements were made by observing the response of the high-Q Whispering
Gallery doublet (WGH) in a Hemex sapphire resonator cooled to 5
K. The doublets initially existed as standing waves at zero field and were
transformed to traveling waves due to the gyrotropic response.Comment: Accepted for publication in Phys. Rev.
Asymptomatic Supraventricular Arrhythmias in Patients Undergoing Dialysis
Aim. Supraventricular arrhythmias (SVA) are associated with high morbidity and mortality. However, little attention is paid to this condition in patients undergoing hemodialysis. The aim of this study was to analyze the long-term relationship of intradialytic SVA, including asymptomatic arrhythmias, with adverse events in a cohort of patients undergoing hemodialysis.Material and methods. An observational prospective study was conducted in a group of patients on hemodialysis with a 10-year follow-up. The study involved 77 patients (42 men and 35 women; mean age 58±15 years) with sinus rhythm, then they were monitored for ECG for six consecutive hemodialysis sessions during recruitment.Results. Arterial hypertension was present in 68.8% of patients, diabetes mellitus in 29.9% of patients. SVA were reported in 38 patients (49.3%); they all had a short-term, asymptomatic character and were terminated independently. Age (hazard ratio [HR] 1.04 per year; 95% confidence interval [CI] 1.00-1.08) and an increase of the atrium (HR 4.29; 95%CI 1.30-14.09) were associated with supraventricular arrhythmia in multidimensional analysis. During an average follow-up of 40 months, 57 patients died, and cardiovascular diseases were the main cause of death (52.6%). Variables associated with all-cause mortality in the Cox model were age (HR 1.04 per year; 95%CI 1.00-1.08), C-reactive protein (HR 1.04 per 1 mg/l; 95%CI 1.00-1.08) and supraventricular arrhythmias (HR 3.21; 95%CI 1.29-7.96). Patients with supraventricular arrhythmias also had a higher risk of nonfatal cardiovascular events (HR 4.32; 95%CI 2.11-8.83) and symptomatic atrial fibrillation during observation (HR 17.19; 95%CI 2.03-145.15).Conclusions. Strong relationships have been established between the presence of supraventricular arrhythmias recorded during ECG during dialysis and symptomatic AF developing in the future. Patients with supraventricular arrhythmias had a larger right atrium. Age and supraventricular arrhythmias are the main variables associated with mortality in dialysis patients
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